The invention relates to a method for measuring unevenness created by grooves and/or long waves in the surface of an object from a measuring platform, wherein the measuring platform and the object are moved relative to each other.
One example for the use of such a method is the measuring of such unevenness on the driving surface of rails in a track bed, designed for rail-bound transport means, e.g. trains, street cars, subways and the like. Due to the rail traffic, unevenness occurs locally and periodically on the rail tops that form the driving surfaces. Unevenness of this type produces structure-born noise and vibrations when the wheels of the rail vehicle roll off, which can lead to noise pollution for the environment as well as noise and vibrations stress for the passengers. The unevenness in the driving surface must be recognized early on because it worsens with increased rail traffic and leads to a considerable reduction in travel comfort and also travel safety. Rails with unevenness in the driving surface are subject to considerable wear and tear and have a much shorter service life than rails without such unevenness of the driving surface. The unevenness of the driving surface, which is defined as grooves with a wave length xcex between 10 mm and 300 mm and as so-called longitudinal waves having a wave length xcex between 300 mm and 3000 mm, must be removed by grinding, milling or planing the rails. A number of measuring methods have been developed for this, which allow measuring any unevenness of the driving surface, that is to say during routine inspection drives as well as for the purpose of a subsequent testing and documentation of the rail surface treatment, which has been carried out. In the process, a so-called arithmetic average rough value Ra according to DIN 4768 is defined for the normal state of the rails, which must not be exceeded over a predetermined rail length L.
According to a conventional method for measuring unevenness of this type on the driving surface of rails (Stuart L. Grassie xe2x80x9cMeasurement of railhead longitudinal profiles: a comparison of different techniques,xe2x80x9d Wear 191, (1996), pages 245-251) such as the traveling chord measuring principle, the distance between the measuring platform and a ruler that touches the rail with its two end points is measured by means of a tracer pin or a sensor that measures without contact. The ruler is pressed by the measuring platform against the rail and is moved together with the measuring platform along the rail. If the profile deviation in a vertical section through the rail surface is a planar curve, then the ruler represents a chord of this curve. The profile is determined from the measured distances, also called arrow heights, which can further be used to compute the roughness of the driving surface. In order to detect all possible wavelengths of the driving surface unevenness, several ruler lengths must be used, which results in extreme disadvantages when realizing the method. Another disadvantage of the method is that the tracer pin must be pressed against the rail, regardless of the measuring platform vibration, which requires a high mechanical expenditure. If an inertial system is attached to the car axle, the measurements are recorded in a coordinate system that is independent of the measuring platform. To be sure, the measuring method is simple, but the measuring system is described with the aid of very many parameters that must be known. The measuring system behavior depends on the speed of the measuring platform, the rail, the type of tie and the track bed material. A local measurement is not possible, but only statistical statements concerning the profile deviation over measured distances of approximately 10 m. Inertial systems furthermore are only operational with sufficient accuracy starting with a minimum speed of the measuring platform of approximately 20 km/h, thus making it impossible to use such measuring systems in connection with slow-moving machines for working the railhead.
It is therefore the object of the invention to provide a method of the aforementioned type as well as a device for use with this method, which method or device permits measurements without making contact, is rugged with respect to the relative movement between measuring platform and object and delivers uniformly good measuring results, independent of the movement speed.
This object is solved with a method for measuring unevenness formed by grooves and/or long waves in a surface of an object by using a measuring platform, including: moving an object and a measuring platform relative to each other; projecting from the measuring platform a light streak that extends in a direction of the movement onto a surface of the object at a fixed projection angle that is tilted relative to a surface normal of the surface; reproducing the light streak on a planar, position-sensitive photo receiver with a plurality of successive instantaneous exposures of the photo receiver, where the photo receiver is fixedly arranged on the measuring platform with a recording angle that is tilted relative to the fixed projection angle; recording the surface along the direction of the movement with a plurality of continuous light-streak images; and determining a surface profile of the surface along the direction of the movement from deformations in the plurality of the light-streak images.
The method according to the invention has the advantage that all unevenness in the object surface can be detected with high measuring accuracy, regardless of the wavelength. The method is continuous and fully automatic and, if used for the driving path of rail traffic means, can be used with extremely slow as well as extremely fast measuring platforms moving along the rails because it does not depend on the speed. Furthermore, it can be used without detraction either together with a working machine for smoothing the rail surface, so as to monitor and document the result of the working operation, or within the framework of inspection drives for testing the condition of the rail surface on a measuring car that is traveling at a high speed (up to 200 km/h). The method according to the invention is insensitive to changes in the distance and a tilting of the measuring platform, relative to the rails, and can thus be used without problems on measuring platforms, which are subjected to vibrations and movements during the measuring operation.
A useful embodiment of the method according to the invention or the device according to the invention for realizing said method, as well as advantageous modifications and embodiments of the invention follow in the detailed description of the invention.
The invention is described in further detail in the following with the aid of an exemplary embodiment, shown in the drawing, of a device for measuring the driving surface unevenness of rails from a measuring platform that moves along the rails.